This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a method and apparatus for mixing milled asphalt and rejuvenating fluid in such rejuvenation.
Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as tar. With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt pavement degrades. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt pavement. Also, much of the degradation occurs within the top two or three inches of the surface.
Traditionally, worn asphalt pavement was not restored but instead was torn up and replaced with new asphalt pavement. This is a costly approach and creates a problem as to what to do with the torn up pavement. Accordingly, techniques and apparatus have been developed for restoring or rejuvenating the top few inches of an asphalt pavement surface.
A typical road resurfacing machine has a heater for heating and softening the asphalt pavement surface as it passes along the surface. Following the heater is a xe2x80x9crakexe2x80x9d or xe2x80x9cscarifierxe2x80x9d which breaks up or xe2x80x9cscarifiesxe2x80x9d the softened pavement. The scarified pavement is generally crushed or xe2x80x9cmilledxe2x80x9d, blended with rejuvenating fluid and optionally additional sand or aggregate and redeposited. The redeposited material is spread out and rolled to create a rejuvenated surface comparable in quality to the original surface before degradation.
In order to produce a rejuvenated surface of high quality, it is important to ensure that an appropriate amount of rejuvenating fluid is added. Generally, a core sample or several core samples are initially taken of the surface to be rejuvenated and a desired ratio of rejuvenating material to milled material is analytically determined.
It is also important to thoroughly intermingle the milled material with the rejuvenating material, which will at least include a fluid but may also include additional sand and/or aggregate.
It is an object of the present invention to provide a method and apparatus for thoroughly blending the milled material with at least the rejuvenating fluid and with any other rejuvenating materials.
A mixer for an asphalt resurfacing machine which has a transport structure to which is mounted a heater for heating an underlying surface, a scarifier following the heater to break up the heated surface, a mill following the scarifier for grinding the scarified surface to form a milled material and prepare the underlying surface to a pre-set depth and a rejuvenating fluid sprayer for introducing a rejuvenating fluid to the milled material. The mixer has a first stage, including a shell which is substantially enclosed but for a downwardly facing bottom opening. An inlet opening extends through a forward face of the shell and faces in a travel direction of the transport structure. The inlet opening receives milled material from the mill. A first stage shaft extends transversely relative to the travel direction and is mounted to the first stage shell for rotation about a first stage shaft axis. A plurality of paddles extend radially from the first stage shaft for blending the rejuvenating fluid with the milled material and to direct the blended material thus formed toward a first stage discharge outlet facing rearwardly relative to the travel direction. The first stage shell is placeable in close proximity to the underlying surface to use the underlying surface as a bottom part thereof. A rotator is provided for rotating the shaft along with the paddles.
The mixer may include a second stage mounted to follow the first stage and receive blended material from the discharge outlet of the first stage. The second stage has a downwardly opening second stage shell extending from the rear of the first stage shell. A second stage shaft is mounted in the second stage shell for rotation about a second stage shaft axis generally parallel to the first stage shaft axis. A plurality of paddles extend substantially radially from the second stage shaft. The paddles are rotatable with the second stage shaft for further blending of the blended material and for directing the blended material toward a second stage discharge opening through the second stage shell which faces rearwardly relative to the travel direction. The second stage also has a rotator for rotating the second stage shaft about the second stage shaft axis.
The rotator may be a motor having a sprocket and chain arrangement linking the motor to the first and second stage shafts.
A method is provided for blending milled material with rejuvenating fluid in an asphalt resurfacing machine having a first pug mill attached to a transport structure associated with the asphalt resurfacing machine in an inverted arrangement in which an open face of the first pug mill is adjacent an underlying surface for the underlying surface to act as a bottom of the pug mill, the first pug mill having a first paddle shaft extending generally transversely relative to a travel direction of the transport structure, the method comprises the steps of:
(i) moving the transport structure along the underlying surface to move the first pug mill in the travel direction;
(ii) receiving the milled material and rejuvenating fluid into the first pug mill through a forwardly facing first inlet;
(iii) blending the milled material with the rejuvenating fluid by rotating the first paddle shaft to cause paddles extending radially therefrom to co-mingle the milled material with the rejuvenating fluid, the paddles being aligned to direct a blended material thus formed toward a rearwardly facing first discharge opening; and,
(iv) allowing the blended material to be discharged through the first discharge opening as the first pug mill moves in the travel direction.
A second pug mill may be attached to the transport structure to follow the first pug mill, the second pug mill being mounted in an inverted arrangement in which an open face thereof is adjacent the underlying surface to utilize the underlying surface as a bottom thereto, the second pug mill having a second inlet- for receiving the blended material discharged from the first discharge opening, the second pug mill having a second paddle shaft generally parallel to the first paddle shaft and having a plurality of paddles extending substantially radially therefrom and the method may include the further steps of:
(v) receiving the blended material into the second pug mill through the second inlet;
(vi) rotating the second paddle shaft to further blend the blended material received from the first pug mill, the paddles being aligned to direct further blended material thus formed toward a rearwardly facing second discharge opening; and,
(vii) discharging the further blended material in a windrow from the second discharge opening.